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<title>WebGL - Planar Projection with lines</title>
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Planar Projection with lines
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  <div id="uiContainer">
    <div id="ui">
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<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="resources/webgl-lessons-ui.js"></script>
<script src="resources/webgl-utils.js"></script>
<script src="resources/m4.js"></script>
<script src="resources/primitives.js"></script>
<!-- vertex shader -->
<script id="vertex-shader-3d" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec2 a_texcoord;

uniform mat4 u_projection;
uniform mat4 u_view;
uniform mat4 u_world;
uniform mat4 u_textureMatrix;

varying vec2 v_texcoord;
varying vec4 v_projectedTexcoord;

void main() {
  // Multiply the position by the matrix.
  vec4 worldPosition = u_world * a_position;

  gl_Position = u_projection * u_view * worldPosition;

  // Pass the texture coord to the fragment shader.
  v_texcoord = a_texcoord;

  v_projectedTexcoord = u_textureMatrix * worldPosition;
}
</script>
<!-- fragment shader -->
<script id="fragment-shader-3d" type="x-shader/x-fragment">
precision mediump float;

// Passed in from the vertex shader.
varying vec2 v_texcoord;
varying vec4 v_projectedTexcoord;

uniform vec4 u_colorMult;
uniform sampler2D u_texture;
uniform sampler2D u_projectedTexture;

void main() {
  vec3 projectedTexcoord = v_projectedTexcoord.xyz / v_projectedTexcoord.w;
  bool inRange = 
      projectedTexcoord.x >= 0.0 &&
      projectedTexcoord.x <= 1.0 &&
      projectedTexcoord.y >= 0.0 &&
      projectedTexcoord.y <= 1.0;
  vec4 projectedTexColor = texture2D(u_projectedTexture, projectedTexcoord.xy);
  vec4 texColor = texture2D(u_texture, v_texcoord) * u_colorMult;
  float projectedAmount = inRange ? 1.0 : 0.0;
  gl_FragColor = mix(texColor, projectedTexColor, projectedAmount);
}
</script>
<!-- vertex shader -->
<script id="color-vertex-shader" type="x-shader/x-vertex">
attribute vec4 a_position;

uniform mat4 u_projection;
uniform mat4 u_view;
uniform mat4 u_world;

void main() {
  // Multiply the position by the matrices.
  gl_Position = u_projection * u_view * u_world * a_position;
}
</script>
<!-- fragment shader -->
<script id="color-fragment-shader" type="x-shader/x-fragment">
precision mediump float;

uniform vec4 u_color;
void main() {
  gl_FragColor = u_color;
}
</script>
<script>
'use strict';

function main() {
  // Get A WebGL context
  /** @type {HTMLCanvasElement} */
  const canvas = document.querySelector('#canvas');
  const gl = canvas.getContext('webgl');
  if (!gl) {
    return;
  }

  // setup GLSL programs
  const textureProgramInfo = webglUtils.createProgramInfo(gl, ['vertex-shader-3d', 'fragment-shader-3d']);
  const colorProgramInfo = webglUtils.createProgramInfo(gl, ['color-vertex-shader', 'color-fragment-shader']);

  const sphereBufferInfo = primitives.createSphereBufferInfo(
      gl,
      1,  // radius
      12, // subdivisions around
      6,  // subdivisions down
  );
  const planeBufferInfo = primitives.createPlaneBufferInfo(
      gl,
      20,  // width
      20,  // height
      1,   // subdivisions across
      1,   // subdivisions down
  );
  const cubeLinesBufferInfo = webglUtils.createBufferInfoFromArrays(gl, {
    position: [
      -1, -1, -1,
       1, -1, -1,
      -1,  1, -1,
       1,  1, -1,
      -1, -1,  1,
       1, -1,  1,
      -1,  1,  1,
       1,  1,  1,
    ],
    indices: [
      0, 1,
      1, 3,
      3, 2,
      2, 0,

      4, 5,
      5, 7,
      7, 6,
      6, 4,

      0, 4,
      1, 5,
      3, 7,
      2, 6,
    ],
  });

  // make a 8x8 checkerboard texture
  const checkerboardTexture = gl.createTexture();
  gl.bindTexture(gl.TEXTURE_2D, checkerboardTexture);
  gl.texImage2D(
      gl.TEXTURE_2D,
      0,                // mip level
      gl.LUMINANCE,     // internal format
      8,                // width
      8,                // height
      0,                // border
      gl.LUMINANCE,     // format
      gl.UNSIGNED_BYTE, // type
      new Uint8Array([  // data
        0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC,
        0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF,
        0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC,
        0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF,
        0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC,
        0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF,
        0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC,
        0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF, 0xCC, 0xFF,
      ]));
  gl.generateMipmap(gl.TEXTURE_2D);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);

  function loadImageTexture(url) {
    // Create a texture.
    const texture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, texture);
    // Fill the texture with a 1x1 blue pixel.
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE,
                  new Uint8Array([0, 0, 255, 255]));
    // Asynchronously load an image
    const image = new Image();
    image.src = url;
    image.addEventListener('load', function() {
      // Now that the image has loaded make copy it to the texture.
      gl.bindTexture(gl.TEXTURE_2D, texture);
      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA,gl.UNSIGNED_BYTE, image);
      // assumes this texture is a power of 2
      gl.generateMipmap(gl.TEXTURE_2D);
      render();
    });
    return texture;
  }

  const imageTexture = loadImageTexture('resources/f-texture.png');  /* webglfundamentals: url */

  function degToRad(d) {
    return d * Math.PI / 180;
  }

  const settings = {
    cameraX: 2.75,
    cameraY: 5,
    posX: 2.5,
    posY: 4.8,
    posZ: 4.3,
    targetX: 2.5,
    targetY: 0,
    targetZ: 3.5,
    projWidth: 1,
    projHeight: 1,
    perspective: true,
    fieldOfView: 45,
  };
  webglLessonsUI.setupUI(document.querySelector('#ui'), settings, [
    { type: 'slider',   key: 'cameraX',    min: -10, max: 10, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'cameraY',    min:   1, max: 20, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'posX',       min: -10, max: 10, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'posY',       min:   1, max: 20, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'posZ',       min:   1, max: 20, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'targetX',    min: -10, max: 10, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'targetY',    min:   0, max: 20, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'targetZ',    min: -10, max: 20, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'projWidth',  min:   0, max:  2, change: render, precision: 2, step: 0.001, },
    { type: 'slider',   key: 'projHeight', min:   0, max:  2, change: render, precision: 2, step: 0.001, },
    { type: 'checkbox', key: 'perspective', change: render, },
    { type: 'slider',   key: 'fieldOfView', min:  1, max: 179, change: render, },
  ]);

  const fieldOfViewRadians = degToRad(60);

  // Uniforms for each object.
  const planeUniforms = {
    u_colorMult: [0.5, 0.5, 1, 1],  // lightblue
    u_texture: checkerboardTexture,
    u_world: m4.translation(0, 0, 0),
  };
  const sphereUniforms = {
    u_colorMult: [1, 0.5, 0.5, 1],  // pink
    u_texture: checkerboardTexture,
    u_world: m4.translation(2, 3, 4),
  };

  function drawScene(projectionMatrix, cameraMatrix) {
    // Make a view matrix from the camera matrix.
    const viewMatrix = m4.inverse(cameraMatrix);

    const textureWorldMatrix = m4.lookAt(
        [settings.posX, settings.posY, settings.posZ],          // position
        [settings.targetX, settings.targetY, settings.targetZ], // target
        [0, 1, 0],                                              // up
    );
    const textureProjectionMatrix = settings.perspective
        ? m4.perspective(
            degToRad(settings.fieldOfView),
            settings.projWidth / settings.projHeight,
            0.1,  // near
            200)  // far
        : m4.orthographic(
            -settings.projWidth / 2,   // left
             settings.projWidth / 2,   // right
            -settings.projHeight / 2,  // bottom
             settings.projHeight / 2,  // top
             0.1,                      // near
             200);                     // far

    let textureMatrix = m4.identity();
    textureMatrix = m4.translate(textureMatrix, 0.5, 0.5, 0.5);
    textureMatrix = m4.scale(textureMatrix, 0.5, 0.5, 0.5);
    textureMatrix = m4.multiply(textureMatrix, textureProjectionMatrix);
    // use the inverse of this world matrix to make
    // a matrix that will transform other positions
    // to be relative this world space.
    textureMatrix = m4.multiply(
        textureMatrix,
        m4.inverse(textureWorldMatrix));

    gl.useProgram(textureProgramInfo.program);

    // set uniforms that are the same for both the sphere and plane
    webglUtils.setUniforms(textureProgramInfo, {
      u_view: viewMatrix,
      u_projection: projectionMatrix,
      u_textureMatrix: textureMatrix,
      u_projectedTexture: imageTexture,
    });

    // ------ Draw the sphere --------

    // Setup all the needed attributes.
    webglUtils.setBuffersAndAttributes(gl, textureProgramInfo, sphereBufferInfo);

    // Set the uniforms unique to the sphere
    webglUtils.setUniforms(textureProgramInfo, sphereUniforms);

    // calls gl.drawArrays or gl.drawElements
    webglUtils.drawBufferInfo(gl, sphereBufferInfo);

    // ------ Draw the plane --------

    // Setup all the needed attributes.
    webglUtils.setBuffersAndAttributes(gl, textureProgramInfo, planeBufferInfo);

    // Set the uniforms we just computed
    webglUtils.setUniforms(textureProgramInfo, planeUniforms);

    // calls gl.drawArrays or gl.drawElements
    webglUtils.drawBufferInfo(gl, planeBufferInfo);

    // ------ Draw the cube ------

    gl.useProgram(colorProgramInfo.program);

    // Setup all the needed attributes.
    webglUtils.setBuffersAndAttributes(gl, colorProgramInfo, cubeLinesBufferInfo);

    // scale the cube in Z so it's really long
    // to represent the texture is being projected to
    // infinity
    const mat = m4.multiply(
        textureWorldMatrix, m4.inverse(textureProjectionMatrix));

    // Set the uniforms we just computed
    webglUtils.setUniforms(colorProgramInfo, {
      u_color: [0, 0, 0, 1],
      u_view: viewMatrix,
      u_projection: projectionMatrix,
      u_world: mat,
    });

    // calls gl.drawArrays or gl.drawElements
    webglUtils.drawBufferInfo(gl, cubeLinesBufferInfo, gl.LINES);
  }

  // Draw the scene.
  function render() {
    webglUtils.resizeCanvasToDisplaySize(gl.canvas);

    // Tell WebGL how to convert from clip space to pixels
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

    gl.enable(gl.CULL_FACE);
    gl.enable(gl.DEPTH_TEST);

    // Clear the canvas AND the depth buffer.
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    // Compute the projection matrix
    const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
    const projectionMatrix =
        m4.perspective(fieldOfViewRadians, aspect, 1, 2000);

    // Compute the camera's matrix using look at.
    const cameraPosition = [settings.cameraX, settings.cameraY, 7];
    const target = [0, 0, 0];
    const up = [0, 1, 0];
    const cameraMatrix = m4.lookAt(cameraPosition, target, up);

    drawScene(projectionMatrix, cameraMatrix);
  }
  render();
}

main();
</script>
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